Quantifying cotton source-sink relationships under layered phosphorus placement with fertigation management

Cotton yield formation is dependent on source-sink capacity and relationships. The present study aimed to investigate the effects of layered phosphorus (P) application combined with drip irrigation on cotton source-sink relationships and yield formation. Two-year field experiments were conducted, employing three P layered application treatments (D1: 5 cm + 15 cm, D2: 15 cm + 25 cm, D3: 5 cm + 15 cm + 25 cm) and three drip irrigation application rates (B25: 0.25/0.75, B50: 0.5/0.5, B75: 0.75/0.25). The control (CK) treatment consisted of 50 % P applied pre-sowing into the 0–25 cm soil depth and 50 % applied through drip irrigation. The results showed that, under B50 and B75 phosphate fertilizer basal dressing ratios, layered fertilization treatments significantly increased source (sink) dry matter (W_max) by 16.93 %-41.30 % (source) and 10.48 %-35.74 % (sink) compared with CK. The maximum source and sink growth rate (S_max) of layered fertilization treatments was also significantly elevated, showing increases of 23.94 %-54.22 % (source) and 10.83 %-41.59 % (sink) over CK. The W_max, S_max, and yield of the layered fertilization treatments exhibited a trend of D2 >D3 >D1 and B50 >B75 >B25. The two-year average yields of the B50(75)D2(D3) treatments were significantly higher than CK, with increases ranging from 6.02 % to 17.65 %. Notably, the B50D2 treatment exhibited a prolonged source growth period, higher source and sink dry matter accumulation, a more balanced source and sink partitioning index, and a relatively balanced source-sink relationship, resulting in higher yields compared with other treatments. Therefore, the B50D2 treatment is recommended as an effective P precision fertilization strategy for cotton cultivation in Xinjiang.